Circuit arrangement for separating electrical signal pulses



Aug. 20, 1940. E. 1.. (3, WHITE 2,211,942

CIRCUIT ARRANGEMENT FOE SEPARATINQELECTRICAL SIGNAL PULSES Filed March 2, 1938 INVENTOR ERIC L- C. WHITE A TTORNEY Patcnted'Aug. 20, 1940 I PATENT OFFICE cracurr ARRANGEMENT FOR SEPARATING auw'rmcsr. srcmu. PULSES Eric Lawrence Casling White, Hillingdon, England, assignor to Electric & Musical Industries Limited, Hayes, Mlddl pany of Great Britain esex, England, a com- Application March 2, 1938, Serial No. 193,401

In Great Brit 11 Claims.

for separating electric signal pulses, and has particular but not exclusive reference to the synchronising pulse separating circuits used in tele- 5 vision systems.v

-In most proposed television systems, the'irame frequency synchronising pulses are distinguished from the line synchronising pulses by greater duration of the former. Separation can thus be effected by means of a low pass filter, but in the case of interlaced scanning systems employing the low pass filter method of separation difllculties arise because the effective time of travel through the filter is afiected by the previous line pulse which occurs alternately at line and halfline intervals so that perfect interlacing is hindered. Any electrical network having a linear response characteristic is subject to the objection mentioned, and in order to eliminate the undesirable effect, it is necessary to include in the network a device such as a diode or other valve, the response characteristic curve of which is nonlinear.

In the specification of co-pending patent application No. 59,022, filed January 14, 1936, an arrangement is described in which the pulses are integrated so that the longer pulses allow a greater potential to be developed across a condenser than that developed by the shorter pulses. The

condenser is discharged by one non-linear element, actually a valve, at the end of each pulse and another non-linear element, a diode,'effects selection by amplitude of the integratedpulses.

The object of the present invention is to provide an alternative circuit arrangement which will effect separation of frame synchronising pulses in such a manner that reliable interlaced scanning can be effected, although it will be seen from the following description that the invention may find application in any electrical signalling system in which pulses of two or more different widths are employed. v

According to the present invention a circuit arrangement for effecting selection from a mixture of electrical signal pulses which are of differing duration of those pulses exceeding a given duration, comprises anetwork to which said mixture of pulses is applied, said network including parallel paths one of which contains a delay network which eiiects delay substantially equal to said given duration, said parallel paths feeding a circuit containing at least one nonlinear device which only gives an output when there is an overlap between the delayed and undelayed pulses March 10, 1937 (01.178-73) This invention relates to circuit arrangements A television receiving systemembodying the invention includes a circuit arrangement for effecting selection of frame synchronising pulses from a mixture of line synchronising pulses and frame synchronising pulses of longer duration 6 than said line synchronising pulses and a network including parallel paths one of which contains a delay network which effects delay greater than the duration of a line synchronising pulse but less than that of a frame synchronising pulse 10 and less than the period between consecutive line pulses, said parallel paths feeding a circuit containing at least one non-linear device which only gives an output when the delayed and undelayed frame pulses overlap. The mixture of l pulses may also include picture signals which are not transmitted by said parallel paths. The non-linear device may be a thermionic valve forming part of a circuit for generating a voltage of saw-tooth waveform or a valve the output of which is used to drive such a circuit and, in particular circuit arrangements embodying the invention, the parallel paths are constituted by separate electron paths in a thermionic valve or in'separate thermionic valves. 1

In order that the invention may be more clearly understood and readily carried into effect, some circuit arrangements embodying the invention will now be more fully described by way of example-with reference to the accompanying drawing in which:

Figs. 1, 2, 3, 4 and 5 are alternative forms of circuit for separating the frame pulses from the mixture of picture signals and line and frame pulses in television receiving systems.

Referring to Fig. 1 of the drawing, and 2 are the input terminals to a pulse separating circuit including triode valves 3 and 4, and a blocking oscillator valve 5. The mixture of signals including picture signals and line and frame synchronising signals are applied to the terminals l and {the picture signals being in the negative sense and the synchronising signals in the positive sense. The grid of the valve 3 is so biased for example, automatically that the valve is unresponsive to the picture signals and only the line and frame synchronising signals are transmitted through that valve to the screen grid of the blocking oscillator valve 5 through a coupling condenser 6. The valve 4 acts similarly to the valve 3, but the signals applied to its grid are delayed by the-network represented by the rectangle 1. Thus, there will be continually applied to the screen grid of the valve 5 one set of line and frame synchronising signals and another identical set of signals displaced in time from the first set. The delay introduced by the network I is such that the line signals in both sets of pulses are always separated and never overlap, but the frame pulses are caused to overlap so that a pulse of increased amplitude is applied to the screen grid of the valve 5. The potentials applied to the electrodes of that valve are such that only a pulse of such increased amplitude will cause it, in conjunction with the associated circuit to generate a current of sawtooth waveform which can be applied in the usual manner to the frame deflecting means connected to terminals 9 and ill of a cathode ray tube.

In the arrangement shown in Fig. 2 of the drawing the two sets of line and frame synchronising signals are applied in a positive sense to the two control grids of a hexode valve ii, delay of one set with respect to the other being introduced by the delay network I. The valve II will only pass anode current when pulses are applied simultaneously to the control grids of the valve, that is to say, during the period of overlap of frame pulses, the output from the valve being applied through a condenser i2 to a terminal i3 connected to a blocking oscillator for generating the frame deflecting saw-tooth waveform. Assuming that the undelayed pulses are applied to the control grid nearest the cathode, pulses for effecting line synchronising may be taken from the screening grid of the hexode shown connected through a condenser to a terminal M.

Fig. 3 shows an arrangement slightly different from that shown in Fig. 2. A triode hexode valve i 5 is employed in place of the valve ii, and it will be seen that inthis case the delayed pulses are applied to the first grid of the hexode portion while the underlayed pulses are applied to the outer control grid which is internally connected to the control grid of the triode portion of the valve. In this case, again, the valve only passes anode current when the frame pulses occur simultaneously on both the control grids of the valve, the output being connected through a condenser IE to a blocking oscillator generating the sawtooth frame deflecting waveform. The anode of the triode portion of the valve is connected through a condenser to terminal l8 to which the oscillator for generating the line deflecting waveform is connected and line pulses are thus provided for this oscillator.

Referring now to Fig. 4 of the drawing, a double diode valve I9 in shown in placed the valves II and ii of Figs. 2 and 3. The delayed and undelayed pulses are applied to the anodes of the double diode in the negative direction but with a suitable bias applied so that the potentials of the anodes are always positive with respect to earth. A resistance 20 which is large compared with the impedance of either diode is connected in the common cathodelead to earth and when delayed and undelayed frame pulsescoincide at the diode anodes, the cathode potential will fall. Drive potentials for a frame deflecting blocking oscillator are, taken from terminals 2!, 22 connected with the upper and lower ends of the resistance 20.

In the arrangement shown in Fig. 4 the delay network is loaded and in order to avoid this the arrangement of Fig. 5 may be adopted. In Fig. 5 instead of a double diode, a double triode valve 23 with a single indirectly heated cathode is shown. The value of the resistance in the cathode lead is such that the potential variations at the cathode follow those of the most positive grid. The delayed and undelayed pulses are applied to the two control grids and drive potentials for a frame deflecting blocking oscillator are taken from terminals 24 and 25. Two separate triodes may, of course, be used instead of the combined valve 23. Again, in Fig. 4, the separate diodes may be used instead of the double diode I9.

I claim:

1. A circuit arrangement for effecting selection of those pulses exceeding a given duration from a mixture of electrical signal pulses which are of differing duration, comprising a network to which said mixture of pulses is applied, said network including parallel paths one of which contains a delay network which eifects delay substantially equal to said given duration, said parallel paths feeding a circuit containing at least one nonlinear device which only gives an output when there is an overlap betweenv the delayed and undelayed pulses.

2. A television receiving system including a circuit arrangement for effecting selection of frame synchronising pulses from a mixture of line synchronising pulses and frame synchronising pulses of longer duration than said line synchronising pulses comprising a network including parallel paths one of which contains a delay network which affects delay greater than the duration of a line synchronising pulse but less than that of a frame synchronising pulse and less than the period between consecutive line pulses, said parallel paths feeding a circuit containing at least one non-linear device which only gives an output when the delayed and undelayed frame pulses overlap.

3. A television receiving system according to claim 2 wherein said mixture of pulses also includes picture signals which are not transmitted by said parallel paths.

4. A circuit arrangement according to claim 1 wherein said non-linear device is a thermionic valve forming part of a circuit for generating a voltage of saw-tooth waveform.

5. A circuit arrangement as included in a television receiving system according to claim 2 wherein said non-linear device is a thermionic valve forming part of a circuit for generating a voltage of saw-tooth waveform.

6. A television receiving system as claimed in claim 2 wherein said mixture of pulses also includes picture signals which are not transmitted by said parallel paths and wherein said nonlinear device is a thermionic valve forming part of a circuit for generating a voltage of saw-tooth waveform.

'7. A circuit arrangement according to claim -1 wherein said parallel paths are constituted by separate electron paths and said non-linear device is a thermionic valve forming part of a sawtooth voltage waveform generating circuit.

8. A circuit arrangement as included in a television receiving system according to claim 2 wherein said mixture of pulses also includes picture signals which are not transmitted by said parallel paths, said parallel paths being constituted by separate electron paths and said nonlinear device being a thermionic valve forming part of a saw-tooth waveform generating circuit.

paths are provided by a multf-grid thermionic valve, the delayed and undelayed pulses-being applied to separate control-grids'o! said valve, the output of which provides pulses for operating a frame deflecting circuit. g 3

10. A television receiving system according to claim 2 wherein saidparallel paths are provided by a multi-electrode thermionic valve of the triode hexode type, the delayed pulses being applied to the control grid nearest the cathode and the undelayed pulses being applied to an outer control grid which is connected with the control grid of. the triode portion of the valve, pulses for operating frame and line deflecting circuits being obtained from the anode of said triode hexode valve and the anode of the triode portion of said valve respectively;

11'. A television receiving system according to claim 2 wherein the said parallel paths'are provided by a thermionic valve having two anodes ERIC LAWRENCE 'oAsLmG 

